What is indexing in mysql and how do we create indexing in
mysql
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Answer / ramesh n
Indexes are created on a per column basis. If you have a
table with the columns: name, age, birthday and employeeID
and want to create an index to speed up how long it takes to
find employeeID values in your queries, then you would need
to create an index for employeeID. When you create this
index, MySQL will build a lookup index where employeeID
specific queries can be run quickly. However, the name, age
and birthday queries would not be any faster.
Indexes are something extra that you can enable on your
MySQL tables to increase performance,cbut they do have some
downsides. When you create a new index MySQL builds a
separate block of information that needs to be updated every
time there are changes made to the table. This means that if
you are constantly updating, inserting and removing entries
in your table this could have a negative impact on performance.
syntax
CREATE TABLE <table name> (
<filed name> <field type>....
)
| Is This Answer Correct ? | 2 Yes | 1 No |
Answer / ramse
Ramesh,
Can you please explain how many type of indexing and how
this really works.
one more thing please explain syntax of index creation.
| Is This Answer Correct ? | 2 Yes | 1 No |
Answer / ramya
Two type of indexing
Spatial indexes (created using SPATIAL INDEX):
1.Available only for MyISAM tables. Specifying a
SPATIAL INDEX for other storage engines results in an error.
2.Indexed columns must be NOT NULL.
3.In MySQL 5.0, the full width of each column is
indexed by default, but column prefix lengths are allowed.
However, as of MySQL 5.0.40, the length is not displayed in
SHOW CREATE TABLE output. mysqldump uses that statement. As
of that version, if a table with SPATIAL indexes containing
prefixed columns is dumped and reloaded, the index is
created with no prefixes. (The full column width of each
column is indexed.)
Nonspatial indexes (created with INDEX, UNIQUE, or PRIMARY KEY):
1.Allowed for any storage engine that supports spatial
columns except ARCHIVE.
2.Columns can be NULL unless the index is a primary key.
3.For each spatial column in a non-SPATIAL index except
POINT columns, a column prefix length must be specified.
(This is the same requirement as for indexed BLOB columns.)
The prefix length is given in bytes.
4.The index type for a non-SPATIAL index depends on the
storage engine. Currently, B-tree is used.
| Is This Answer Correct ? | 0 Yes | 0 No |
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